1. Field of the Invention
This invention relates generally to drill pipe protectors, and more particularly to a drill pipe protector having an inner hub attached to the drill pipe exterior and an outer buffer ring encircling the inner hub in radially spaced relation which allows relative rotation between the drill pipe and the outer buffer ring when the outer buffer ring engages the interior of the casing in which the drill pipe is rotating.
2. Brief Description of the Prior Art
Elastomer drill pipe protectors installed on drill pipe to prevent casing wear by the tool joint connections are commonly used in rotary drilling operations. Conventional drill pipe protectors are in the form of a hinged, two-piece semi-cylindrical collar or sleeve made of rubber or other elastomeric material which is secured to an inner steel skeleton, also known as a cage. In transverse cross section, the hinged semi-cylindrical segments of the drill pipe protector form an open "C"-shaped configuration which allows the protector to be clamped around the drill pipe. The drill pipe protector is usually installed on the drill pipe near a tool joint connection. Closure and clamping of the segments onto the drill pipe is commonly achieved by driving a tapered latch pin through interlocking loops on the adjacent ends of the open C-shape which acts as a wedge to provide a tight grip on the drill pipe.
The outer diameter of the drill pipe protector is larger than the diameter of the tool joints of the drill pipe to prevent the tool joints from abrading the interior of the casing wall. When installed, the drill pipe protectors firmly grip the drill pipe and can resist several thousand pounds of side load or axial force without slipping on the drill pipe.
However, most prior art drill pipe protectors are subjected to high torque loads when their outer surface engages the interior of the casing in which the drill pipe is rotating, because there is no relative rotation between the drill pipe and the drill pipe protector. This often results in high torque loads in the drill string, prevention of rotation of the drill string, binding, or separation of the elastomeric material from the interior steel skeleton or cage.
These problems are aggravated by high side loading and torque loads encountered in deviated and horizontal drilling operations and conventional drill pipe casing protectors of unitary construction which are clamped tightly on the drill pipe are unsuitable for use in deviated and horizontal drilling operations.
There are several patents which disclose various drill pipe protectors.
Williams, U.S. Pat. No. 3,741,252 discloses a C-shaped drill pipe protector having a split sleeve sheath formed of thermoplastic material bonded to a metallic core which is clamped to the drill pipe by a tapered latch pin received through interlocking loops on the adjacent ends of the open C-shape. shape. A rubber sleeve insert is bonded to the interior diameter of the protector and is sandwiched between the exterior of the drill pipe and the interior diameter of the protector to prevent corrosion. There is no inner hub or relative rotation between the drill pipe and protector.
Hoon et al, U.S. Pat. No. 3,894,779 discloses a C-shaped drill pipe protector having a split sleeve sheath formed of elastomeric material bonded to a stretchable perforated metal core which is clamped to the drill pipe by a tapered latch pin received through interlocking loops on the adjacent ends of the open C-shape. The elastomeric material fills the perforations of the stretchable metal core and overlie the inner surface of the metal core. There is no inner hub or relative rotation between the drill pipe and protector.
Broussard, U.S. Pat. No. 3,894,780 discloses a hinged drill pipe protector having a pair of C-shaped segments formed of elastomeric material bonded to a metal core and joined by a hinge along one side. The opposed side has a pair of outwardly diverging tabs along opposed sides which are drawn together by a tapered latch which slides downwardly the tabs to secure the protector onto the pipe. The exterior of the protector has a series of vertical slots to allow drilling fluid to flow past the protector during drilling operations. There is no inner hub or relative rotation between the drill pipe and protector.
Sutko et al, U.S. Pat. No. 3,929,388 discloses a segmented pipe protector having a split inner steel cylinder which fits around the drill pipe and a concentric split outer steel cylinder which are secured together by a corrugated metal band disposed therebetween. The longitudinal ends of the C-shaped outer cylindrical segments have interfitting hooks along opposed sides which receive tapered pins to clamp the protector onto the drill pipe. There is no inner hub or relative rotation between the drill pipe and protector.
Fox et al, U.S. Pat. No. 4,042,023 discloses a C-shaped segmented control line protector formed of elastomeric material bonded to a metal cage. The longitudinal ends of the C-shaped members have interfitting projections which receive tapered pins to clamp the protector onto the drill pipe. The exterior of the control line protector has radially extending vertical ribs which are slotted to receive one or more control lines. There is no inner hub or relative rotation between the drill pipe and protector.
Swain et al, U.S. Pat. No. 4,266,578 discloses a hinged drill pipe protector having a pair of C-shaped segments formed of elastomeric material bonded to a metal core and joined by a hinge along one side. A thin layer of rubber is bonded to the interior of the metal core. The longitudinal sides of the segments opposite the hinge have interfitting projections which receive a tapered pin to clamp the protector onto the drill pipe. There is no inner hub or relative rotation between the drill pipe and protector.
Derouin, U.S. Pat. No. 4,384,626 discloses a clamp-on drill pipe stabilizer having a metal gripping sleeve with slotted and tapered ends forming fingers, a metal stabilizer body which carries the metal sleeve, a tapered lower end to engage the tapered lower end of the sleeve and a threaded upper end, and a lock nut threadedly engaged in the upper end of the stabilizer which engages a taper ring. The locknut forces the gripping sleeve downward to compress the fingers of the gripping sleeve inwardly to engage the exterior of the drill pipe. There is no inner hub and no elastomeric outer member, and there is no relative rotation between the drill pipe and protector when the lock nut is tightened.
Odell, U.S. Pat. No. 4,398,772 discloses a C-shaped drill pipe protector having a split sleeve sheath formed of elastomeric material bonded to a metallic core and interfitting projections along one side which receive a tapered pin to clamp the protector onto the pipe. The interior of the protector has a bead at the top and bottom ends to form a hydraulic seal between the exterior of the drill pipe and the protector. There is no inner hub or relative rotation between the drill pipe and protector.
Krueger et al, U.S. Pat. No. 5,069,297 discloses a pipe protector having a C-shaped sleeve sheath formed of elastomeric material bonded to a metallic core and interfitting projections along one side which receive a latch pin to secure the protector onto the pipe. An upper and lower split ring bearing are clamped around the drill pipe at the top and bottom of the protector. The interior of the protector has a series of longitudinal grooves defining longitudinal wedges which are angled between the vertical grooves to reduce frictional drag on the drill pipe. The elastomeric sleeve rotates with the drill pipe, but when the exterior of the sleeve engages the wall of the casing, the sleeve stops rotating, or slightly rotates, and allows the drill pipe to continue rotating inside the sleeve due to the configuration of the grooved interior aided by the drilling fluid. Although there is some relative rotation between the drill pipe and the elastomeric protector due to the reduced frictional engagement of longitudinal grooves and wedges on the interior of the protector, there is no inner hub or relative rotation between the drill pipe and an inner hub.
The present invention is distinguished over the prior art in general, and these patents in particular by a drill pipe casing protector having an inner hub member releasably secured to the exterior of a drill pipe to rotate therewith and an outer buffer ring rotatably mounted on the inner hub to allow relative rotation between the drill pipe and the outer buffer ring when the outer buffer ring engages the interior of the casing in which the drill pipe is rotating to prevent abrasive wear between the drill string and the interior of the casing. The inner hub is formed of semi-cylindrical elastomer segments which are clamped around the drill pipe, each having a metallic semi-cylindrical cage element embedded therein and a semi-cylindrical low friction bearing surface on the exterior thereof. A tapered wedge pin draws the elastomer segments radially inward to firmly grip the drill pipe and secure the inner hub member thereto. The outer buffer ring is also formed of semi-cylindrical elastomer segments each having a metallic semi-cylindrical cage element embedded therein which encircle the inner hub bearing surface in radially spaced relation to allow relative rotation therebetween. The outer buffer ring prevents contact between the exterior of the drill pipe and the interior of the casing, and the drill string and inner hub rotate together relative to the outer buffer ring when it is frictionally engaged with the interior of the casing. Drilling fluid provides lubrication between the inner hub member and outer buffer ring.